paper: consider release channel when selecting version/build (#2902)

Dockerfile

@@ -47,7 +47,7 @@ RUN easy-add --var os=${TARGETOS} --var arch=${TARGETARCH}${TARGETVARIANT} \
   --var version=${MC_SERVER_RUNNER_VERSION} --var app=mc-server-runner --file {{.app}} \
   --from ${GITHUB_BASEURL}/itzg/{{.app}}/releases/download/{{.version}}/{{.app}}_{{.version}}_{{.os}}_{{.arch}}.tar.gz
 
-ARG MC_HELPER_VERSION=1.38.16
+ARG MC_HELPER_VERSION=1.39.0
 ARG MC_HELPER_BASE_URL=${GITHUB_BASEURL}/itzg/mc-image-helper/releases/download/${MC_HELPER_VERSION}
 # used for cache busting local copy of mc-image-helper
 ARG MC_HELPER_REV=1

docs/types-and-platforms/server-types/paper.md

@@ -1,10 +1,20 @@
-Enable Paper server mode by adding a `-e TYPE=PAPER` to your command-line.
+A [PaperMC server](https://papermc.io/) can be automatically downloaded, upgraded, and run by setting the environment variable TYPE to "PAPER".
 
-By default, the container will run the latest build of [Paper server](https://papermc.io/downloads) but you can also choose to run a specific build with `-e PAPERBUILD=205`.
+By default, the container will find and download the latest build for the `VERSION` chosen. If `VERSION` is not specified, then the latest Minecraft version released by PaperMC is selected. Along with a specific `VERSION`, a specific Paper build can be selected by setting the environment variable `PAPER_BUILD`. 
 
-    docker run -d -v /path/on/host:/data \
-        -e TYPE=PAPER \
-        -p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
+To allow for the selection of experimental builds, set `PAPER_CHANNEL` to "experimental", otherwise only release/default channel builds are selected.
+
+!!! example
+
+    ```
+    docker run ... -e TYPE=PAPER ... 
+    
+    docker run ... -e TYPE=PAPER -e VERSION=1.20.6 ... 
+    
+    docker run ... -e TYPE=PAPER -e VERSION=1.20.6 -e PAPER_BUILD=140 ... 
+    
+    docker run ... -e TYPE=PAPER -e PAPER_CHANNEL=experimental ... 
+    ```
 
 If you are hosting your own copy of Paper you can override the download URL with `PAPER_DOWNLOAD_URL=<url>`.
 

scripts/start-deployPaper

@@ -6,7 +6,8 @@ set -o pipefail
 handleDebugMode
 
 : "${PAPER_PROJECT:=paper}"
-: "${PAPERBUILD:=}"
+: "${PAPER_BUILD:=${PAPERBUILD:-}}"
+: "${PAPER_CHANNEL:=default}"
 : "${PAPER_DOWNLOAD_URL:=}"
 : "${PAPER_CUSTOM_JAR:=}"
 : "${PAPER_CONFIG_DEFAULTS_REPO:=https://raw.githubusercontent.com/dayyeeet/minecraft-default-configs/main}"
@@ -34,9 +35,10 @@ else
     --results-file="$resultsFile"
     --project="$PAPER_PROJECT"
     --version="$VERSION"
+    --channel="$PAPER_CHANNEL"
   )
-  if [[ $PAPERBUILD ]]; then
-    args+=(--build="$PAPERBUILD")
+  if [[ $PAPER_BUILD ]]; then
+    args+=(--build="$PAPER_BUILD")
   fi
   if ! mc-image-helper install-paper "${args[@]}"; then
       log "ERROR: failed to download $PAPER_PROJECT"